The processes of vectorial cell movement (chemotaxis) and specific intercellular cohesion (cell recognition) are common to all eukaryotic developmental systems including neuronal differentiation. The cellular slime molds represent a model system in which both of these morphogenetic functions occur on a short time scale and large number of identical cells can be obtained (greater than 10 to the 11th power) and differentiated at will. Species specific intercellular cohesion involves the interaction of cell surface carbohydrate binding proteins with oligosaccharide receptors. Purification and characterization of both components from D. discoideum and P. pallidum cells is proposed, as well as comparison of the structure of soluble intracellular binding proteins with those obtained from the cell surface. The developmental dynamics of binding proteins and receptors will also be studied in terms of the regulation of their appearance, function and turnover on the cell surface. The cell surface receptor for cyclic AMP which functions in chemotaxis will be purified and its structure, function and topography will be studied. Photoaffinity labeling of this receptor and other nucleotide binding proteins of developmental importance will aid their identification, purification and characterization. The cell surface and soluble, extracellular cyclic nucleotide phosphodiesterases will be purified and structurally compared. All purified components of the morphogenetic apparatus will be subjected to structural analysis, including amino acid sequencing when possible, and emphasis will be placed on correlating functional, topographical and regulatory information with regions of defined structure. The sum of these studies will provide a detailed mechanistic description of the processes of chemotaxis and specific cell recognition in a simple eukaryotic system, thus focussing a conceptual and methodological basis for the study of more complex systems.